Answer: D
Explanation: An organism's genetic makeup is called its genotype, and it reflects all of the alleles, or forms of the gene, that are carried by the organism. Consequently, a test cross can help determine whether a dominant phenotype is homozygous or heterozygous for a specific allele.
The term "phenotype" refers to the observable physical properties of an organism; these include the organism's appearance, development, and behavior. An organism's phenotype is determined by its genotype, which is the set of genes the organism carries, as well as by environmental influences upon these genes.
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